# How to reduce PDF file size
Canonical HTML: [https://pdfpix.com/guides/how-to-compress-a-pdf/](https://pdfpix.com/guides/how-to-compress-a-pdf/)
Open the compress tool, drop the file in, type the size you want in KB, and download the result. The part worth reading is what happens next. A PDF is heavy for one of three reasons, and which reason you have decides how much weight comes off. Find the reason first, then set the number.
## The three things that make a PDF big
A PDF is heavy for one of three reasons. Find yours before you set a number, because the reason decides how much weight comes off.
1. Scanned pages. Every page is a photograph of paper, so the file weighs what the photographs weigh, and the text on them is not text at all.
2. Placed images. A report with eight camera photos in it carries eight camera photos, at a resolution no printer and no screen will ever use.
3. Embedded fonts and leftover structure. A font program usually ships every glyph it was designed with, and a document usually draws a few hundred of them. Old revisions and orphaned objects sit in the file after edits and never get cleaned out. This one is real but it is rarely the whole story.
Tell them apart in five seconds. Open the file and try to select a line of text with the cursor. If the text highlights, the pages are not scans and the weight is in the pictures or the fonts. If nothing highlights, the page is an image and the scan is the file.
## What the tool does about each one
[The compress tool](https://pdfpix.com/compress-pdf/) runs four methods against your file at the same time and keeps whichever result is smallest and still passes its check. The structural method rebuilds the document into a fresh file, dropping orphaned objects and old revisions. The image method re-encodes the placed images at 150 dpi with mozjpeg at quality 75. The font method subsets each embedded TrueType down to the glyphs the pages actually draw.
The fourth is the raster method, and it is the only one that touches the page itself. It renders each page at 150 dpi and redraws the page's own text invisibly on top, so the words stay selectable and searchable even though the picture underneath is now an image. It starts only when no other method reached your number, and it gives up early when its own projection cannot beat a candidate another method already holds.
On the public run of 843 cases, each one file at one target, the structural method won 173, the font method 79, the image method 230 and the raster method 361. Which one wins on your file depends on which of the three problems it has, and the result names the winner.
## Type a size, not a quality level
Most tools give you a slider named low, medium and high, which tells you nothing about the file you get. This one takes a number in KB and works toward it. One KB is 1,024 bytes here, so [a 200 KB target](https://pdfpix.com/compress-pdf/200kb/) means the output lands under 204,800 bytes.
If an upload form counts a kilobyte as a flat thousand bytes, its cap is 4,800 bytes tighter than that. When a file that reads as the right size still gets refused, set the target about 3% lower and run it again.
## How much usually comes off
Across the 843 public cases the median reduction was 72.5% of the source bytes and the top tenth reached 97.1%. No output came back larger than the file it started from.
Document kind decides the size per page. At the smallest setting a text page comes down to about 14 KB, a page of text with pictures to about 37 KB, a fax-era scan page to about 29 KB and a phone photo of a page to about 18 KB. Multiply by your page count and you know what number to ask for.
## Check the result before you send it
Nothing ships unread. Every candidate is opened again and its text is compared against the source, and any candidate that lost more than 2% of the non-space characters is thrown away rather than offered to you. On the public run, every one of the 554 cases that carried text kept at least 99.99% of its characters.
The result names the size it reached and the method that won, so you know what you are sending before you send it.
From here, [the quality guide](https://pdfpix.com/guides/compress-pdf-without-losing-quality/) covers which methods cost you nothing and which ones cost you detail. [The compress hub](https://pdfpix.com/guides/compress/) lists the rest of the cluster, including phones, very large files and merged documents.
## Common limits
Every cap a form is likely to name has its own page, and each page says what the number means in bytes and how many pages fit under it.
| Cap | Text pages that fit | Phone photo pages that fit | Page |
| --- | --- | --- | --- |
| 20 KB | 1 | 1 | [Compress PDF to 20 KB](https://pdfpix.com/compress-pdf/20kb/) |
| 50 KB | 3 | 2 | [Compress PDF to 50 KB](https://pdfpix.com/compress-pdf/50kb/) |
| 100 KB | 7 | 5 | [Compress PDF to 100 KB](https://pdfpix.com/compress-pdf/100kb/) |
| 150 KB | 10 | 8 | [Compress PDF to 150 KB](https://pdfpix.com/compress-pdf/150kb/) |
| 200 KB | 14 | 11 | [Compress PDF to 200 KB](https://pdfpix.com/compress-pdf/200kb/) |
| 250 KB | 17 | 13 | [Compress PDF to 250 KB](https://pdfpix.com/compress-pdf/250kb/) |
| 300 KB | 20 | 16 | [Compress PDF to 300 KB](https://pdfpix.com/compress-pdf/300kb/) |
| 400 KB | 25 | 20 | [Compress PDF to 400 KB](https://pdfpix.com/compress-pdf/400kb/) |
| 500 KB | 35 | 25 | [Compress PDF to 500 KB](https://pdfpix.com/compress-pdf/500kb/) |
| 800 KB | 55 | 40 | [Compress PDF to 800 KB](https://pdfpix.com/compress-pdf/800kb/) |
| 1 MB | 70 | 55 | [Compress PDF to 1 MB](https://pdfpix.com/compress-pdf/1mb/) |
| 2 MB | 140 | 110 | [Compress PDF to 2 MB](https://pdfpix.com/compress-pdf/2mb/) |
| 3 MB | 210 | 170 | [Compress PDF to 3 MB](https://pdfpix.com/compress-pdf/3mb/) |
| 4 MB | 290 | 220 | [Compress PDF to 4 MB](https://pdfpix.com/compress-pdf/4mb/) |
| 5 MB | 360 | 280 | [Compress PDF to 5 MB](https://pdfpix.com/compress-pdf/5mb/) |
| 10 MB | 730 | 570 | [Compress PDF to 10 MB](https://pdfpix.com/compress-pdf/10mb/) |
The two people ask for most are the mail attachment cap, where you [compress a PDF to 1 MB](https://pdfpix.com/compress-pdf/1mb/), and the government upload field, where you [compress a PDF to 150 KB](https://pdfpix.com/compress-pdf/150kb/). The rest of this cluster covers the cases the number alone does not: [changing a PDF to a specific size](https://pdfpix.com/guides/change-pdf-file-size/) when a form names a floor or a ceiling, [compressing a large PDF](https://pdfpix.com/guides/compress-a-large-pdf/) when memory is the limit, [compressing on a phone](https://pdfpix.com/guides/compress-a-pdf-on-your-phone/), and [merging first and compressing once](https://pdfpix.com/guides/merge-and-compress-pdfs/) when the document arrives in parts.
## Questions and answers
### How do I reduce PDF file size without installing anything?
Open the compress page in a browser and drop the file on it. The engine is JavaScript and WebAssembly and runs inside the tab, so the document never leaves the machine, no account is needed and there is nothing to install or remove afterwards.
### Which of the four methods will shrink my file?
Whichever one matches your problem, and you do not have to choose. All four run and the smallest verified result wins. On the public run, structural won 173 cases, fonts 79, the image method 230 and raster 361.
### How much smaller does a PDF usually get?
Median 72.5% off the source bytes across 843 public cases, with the top tenth at 97.1% or more. Files with heavy pictures give back the most.
### Is there a page limit or a file size limit?
The tool sets no fixed cap. The limit is the memory of the browser tab, which depends on the device. On an iPhone 16 Pro class phone the tab is capped at 2 GiB, and a 300 page run at 150 dpi finished on that phone without being killed.
### Can you compress a PDF twice?
Yes, and the second pass gives back little. After the first run the lossless methods have nothing left to rebuild or subset, so only the image methods still have room, and every pass re-encodes the pictures again. Compress once, against the number you actually need.
## Related pages
- [Compress PDF](https://pdfpix.com/compress-pdf/): Make a PDF smaller without turning its text into a picture. The file stays in your browser. No upload, no account needed.
- [Compress PDF to 200 KB](https://pdfpix.com/compress-pdf/200kb/): Get this PDF under 200 KB because a form will not accept anything larger. The file stays in your browser. No upload, no account needed.
- [How to compress a PDF without losing quality](https://pdfpix.com/guides/compress-pdf-without-losing-quality/): Cut the file size without wrecking the text or the images. Free, in your browser, with Compress PDF without losing quality.
- [Compress large PDF files](https://pdfpix.com/guides/compress-a-large-pdf/): Deal with a PDF too big for the usual tools. Free, in your browser, with Compress large PDF.
- [Compress a PDF on mobile](https://pdfpix.com/guides/compress-a-pdf-on-your-phone/): Shrink a PDF on a phone without installing anything. Free, in your browser, with Compress PDF.
- [Change PDF file size](https://pdfpix.com/guides/change-pdf-file-size/): Hit an exact file size a form demands. Free, in your browser, with Compress PDF.
- [Compress multiple PDFs into one](https://pdfpix.com/guides/merge-and-compress-pdfs/): Join several PDFs and keep the result under a size limit. Free, in your browser, with Merge PDF.
- [Compress PDF to 1 MB](https://pdfpix.com/compress-pdf/1mb/): Get this PDF under 1 MB, the most common attachment and portal limit. The file stays in your browser. No upload, no account needed.
- [Compress PDF to 150 KB](https://pdfpix.com/compress-pdf/150kb/): Get this PDF under 150 KB for a government upload field. The file stays in your browser. No upload, no account needed.
- [Make a PDF smaller](https://pdfpix.com/guides/compress/): Find the right guide for making a PDF smaller. Every guide on the job, sorted by the problem you have.